Instruments allowing the measurement of atmospheric pressure, known as barometers, have been known for the past 350 years or so. The first such instruments comprised a tube filled with water suspended above a reservoir of water whereby the height of the column of water within the tube falls until the weight of water within the tube offsets the pressure exerted by the atmosphere on the body of the reservoir.
A significant improvement to this type of barometer came about when the fluid within the tube and reservoir was replaced with mercury (for example, the Fortin barometer). Due to the much greater density of mercury, the required tube length required to counterbalance atmospheric pressure for a given tube diameter is corresponding much shorter, at least 84 cm compared to the approximately 10 m tube lengths required for water based Fortin-like barometers. Fortin barometers are highly accurate, with the change in column length for a given change in pressure being largely linear, and give an absolute value for the atmospheric pressure.
In the current political and environmental climate, there is a general desire to replace instruments containing mercury, such as Fortin barometers, with mercury free alternatives. The alternative types of barometers currently available, such as aneroid barometers, the Sympiesometer, quartz Bourdon instruments and electronic instruments, do not measure absolute pressure as such and each requires separate, reference measurements to be taken, leading to the instruments being complicated to use and requiring care when the instruments are set up and operated.
Accordingly, it is an object of the invention to provide an absolute barometer which does not contain mercury.